Peripheral and Central Interactions in Energy Balance (Jeffrey S. Flier, MD, Principal Investigator, Beth Israel Deaconess Medical Center). Obesity and related disorders such as Type II diabetes mellitus are major healthcare issues in the United States, and decreasing their incidence in adults and children would have profound social and economic ramifications. For this to occur, an increased understanding of the mechanisms controlling food intake and body weight is essential. There has been tremendous recent progress in elucidating critical metabolic signals and the pathways in the brain and in peripheral tissues in which these signals act. In the past grant period the projects in this program investigated the central and peripheral actions of leptin. This included the neural pathways activated by leptin and the cellular pathways engaged by leptin in the CNS and skeletal muscle. We also examined the effects of manipulation of leptin receptors in specific neuronal cell groups as well as the deletion of specific neuropeptide genes on energy homeostasis. We offer 5 individual proposals that utilize state of the art genetic, physiological, biochemical, and neuroanatomic techniques to investigate the actions of critical metabolic cues including leptin, ghrelin, and glucocorticoids in the regulation of food intake, energy expenditure, and body weight. These studies will extend from molecular mechanisms of action to systems based studies to understand the physiological importance of these hormones through specific neural circuits. Our proposal consists of 5 individual projects and 3 cores. Project 1 will use functional neuroanatomy to assess the hypothesis that the recently identified hormone ghrelin acts through similar pathways as leptin. It will also use a novel model of orexin deficiency to assess the role of orexin neurons in regulating coordinated autonomic responses to changing levels of ghrelin and leptin. Project 2 will assess the role of melanin concentrating hormone (MCH) in mediating the coordinated autonomic responses of leptin. This will include the use of a novel mouse that lacks MCH and leptin. This project will also assess the interactions of MCH with dopaminergic systems. Project 3 will focus on neuron-specific manipulation of leptin receptors. These studies will include both gene deletion and gene reactivation approaches using transgenic delivery of cre- and flp-recombinase and using AAV delivery of cre- and tiprecembinase, to identify critical first-order, leptin-responsive neurons responsible for initiating leptin's anti-obesity actions. Project 4 will assess the biologic significance of the AMP-activated protein kinase (AMPK) pathway in mediating the central and peripheral effects of leptin on energy homeostasis. This will include specific neuronal alterations of AMPK activity on body weight homeostasis as well as studies to determine the molecular mechanisms by which leptin affects AMPK activity. Project 5 will define the role of glucocerticoid action in specific tissues or cells and neurons. This will include the modulation of GC metabolism by the enzyme 1 ll3HSD1 in peripheral (adipose) and central (hypothalamic) sites involved in regulating energy balance. It will also use genetically modified mice to identify the specific role of direct GC action in adipose tissue and in hypothalamic neural circuits that regulate energy balance. Core A will be an administrative core. Core B will be a Neuroanatomy Core and Core C will be a Physiology Core. Together, these projects will continue to leverage the collaborative efforts and expertise of investigators in Boston and will greatly increase the understanding of the central circuits regulating body weight. PERFORMANCE SITE(